1. Field of the Invention
The present invention relates to new polyamines prepared from (cyclo)aliphatic polyamines and unsaturated oligoesters having an average of 2 to 4 double bonds per molecule, and to their use in combination with blocked polyisocyanates as binders for coating compositions.
2. Description of the Prior Art
Polyhydroxyl compounds, e.g. polyester polyols or polyacrylate polyols, are used as reactants for blocked polyisocyanates in storage-stable one-component stoving lacquers. There have been many attempts to reduce the baking temperature of these lacquers, which is approx. 170.degree. C. Suitable catalysts, such as organic tin compounds or tertiary amines, bring about a reduction of the baking temperature to approx. 150.degree. C., but this is not sufficient. The fact that catalysts also catalyze the reverse reaction at excessively high temperatures, which may occur when the baking temperature is exceeded due to production-related reasons, is also a disadvantage.
Although the desired low baking temperature of approx. 120 to 140.degree. C. may be achieved with new blocking agents having a lower unblocking temperature (EP-A 159,117, which corresponds to U.S. Pat. No. 4,976,837), the coating compositions do not usually have sufficient storage stability.
Therefore, there is a need for a co-reactant for blocked polyisocyanates, which can be used for the preparation of one-component polyurethane stoving lacquers and which not only has a high level of reactivity with the blocked polyisocyanates, but also has good storage stability in combination with blocked polyisocyanates.
It is known from U.S. Pat. No. 3,715,335 to react unsaturated polyesters with diamines having a primary and a tertiary amino group, to optionally allow said reaction products to continue to react with diamines having two primary amino groups, and to quaternize the products at the tertiary nitrogen atoms with epichlorohydrin. The resulting products are recommended as additives for the preparation of paper and as flocculation aids.
EP-A 273,243 describes both polyester polyols containing amino and amide groups which are prepared by reacting unsaturated polyester polyols with low molecular weight polyamines having two primary amino groups, and the use of said products for the preparation of poly(urea)urethanes which are particularly suitable as adhesives. The polyester polyols used for the reaction with diamines are the known unsaturated polyester polyols having a relatively high molecular weight and an OH number of about 10 to 500 mg KOH/g. The polyester polyols are obtained by reaction of polyvalent, preferably divalent .alpha.,.beta.-unsaturated carboxylic acids and/or their anhydrides with polyol compounds. Modified polyester polyols having an OH number of 50 to 500, preferably 150 to 350 mg KOH/g and a total nitrogen content of 1 to 7 wt. %, preferably 2 to 5.5 wt. %, are described as being particularly suitable for adhesive applications. A weight ratio of polyamine to polyester polyol of 0.5:100 to 30:100, preferably 4:100 to 15:100 should be maintained for modification.
It has now been found that special low molecular weight oligoesters may be prepared either by transesterification of di(cyclo)alkyl esters of maleic or fumaric acid with di-, tri- or tetraols or by esterification of maleic anhydride, maleic or fumaric acid with di-, tri- or tetraols and monoalcohols. The oligoesters contain a statistical average of 2 to 4 double bonds per molecule and may be reacted, optionally in admixture with other unsaturated compounds, with (cyclo)aliphatic diamines by the Michael addition (addition of CH-acidic compounds and amines to vinyl carbonyl compounds). New polyamines are obtained which, when combined with blocked polyisocyanates, yield storage-stable, one-component binder combinations which require substantially lower baking temperatures for cross-linking when compared to known one-component polyurethane (PUR) binders.